Cell based analysis can be carried out by staining cells with a specific reagent and inspecting the cell population in a microscope. For imaging-based cell diagnostics, e.g. using a microscope, a camera and a software application for image analysis and diagnosis, it is important to create a monolayer of separated cells to avoid misinterpretations due to cell overlap. One such method has been known for many years and involves scraping a volume of the relevant fluid, e.g. blood, over a glass slide by hand (smear). For an integrated closed cartridge this process cannot be used. Instead capillary filling of narrow channels can be used.
It is known from U.S. Pat. No. 6,599,475-B1 to provide a plastic optical cuvette for creating a thin monolayer of red blood cells for microscopic analysis. A number of compartments are provided connected in series and separated by separating walls. These walls each allow flow of only some of the red blood cells, to achieve red blood cell dilution, so that a monolayer of isolated red blood cells is achieved in the last of the compartments. To achieve a constant thickness across the whole cuvette, the separating walls have weld features and a transparent lid is welded to the top. A compartment may have dimensions 600×600×3 micrometers. For applications like analysis of blood samples for the malaria parasite, a large volume of blood needs to be analysed to achieve the required detection limit. With layer thicknesses of the order of the dimensions of red blood cells (5 μm) this means that large surface areas (square cms) need to be inspected.
U.S. Pat. No. 6,165,739-A1 describes a glass or plastic slide for laser cytometry having a number of capillary gap chambers. A fluid sample can enter all chambers simultaneously from a reservoir. A different reactant is provided in each chamber to enable multiple simultaneous reactions.